DVD - WinDvd 7 Platinum compare to PowerDvd 6 Ultra.
WinDvd at least 15% better picture and at least 75% better audio than PowerDvd.
BR-DVD - I think PowerDvd is better than WinDvd. The reason why I am saying this is Core is doing a very poor jobs on WinDvd.
The only thing I can say is try both - Free Trail Version I planning to buy the Pioneer BDC-2202 it comes with Windvd BR software. I don't know how well it works.

DVD - WinDvd 7 Platinum compare to PowerDvd 6 Ultra.
WinDvd at least 15% better picture and at least 75% better audio than PowerDvd.
BR-DVD - I think PowerDvd is better than WinDvd. The reason why I am saying this is Core is doing a very poor jobs on WinDvd.
The only thing I can say is try both - Free Trail Version I playing to buy the Pioneer BDC-2202 it comes with Windvd BR software. I don't know how well it works.

In terms of Blu-ray compatibility the answer is easy .... neither! both PowerDVD and WinDVD suck, especially WinDVD. For humorous proof just read the release notes for the single WinDVD patch released. It says the patch will "improve" the compatibility with existing titles .... not fix. Arcsoft releases frequent patches to address the "Disk Won't Play Issues" that are very common for newly released thank to the flawed efforts of devs to address piracy concerns.

But, there is one more concern and that is regular DVD playback ... Arcsoft still sucks in this aspect ... some DVDs have skipping and stuttering (BSG Season 4 is an example) whereas WinDVD is the clear winner in this area.

Currently best bang for the buck is WinDVD or free alternatives for regular DVDs and Arcsoft TMT for Blu-Ray because there is nothing worse than porking out 30$ for a Blu-ray that won't play and not being able to return it or even exchange it for a regualr DVD at your loss (HMV Canada won't do this)

I have been waiting 3 months for WinDVD to play Wall-E Blu-Ray with no end in sight and Wall-E is a huge release. Arcsoft plays it perfectly

I suggest you wait another week, and purchase powerdvd9 ultra instead. I have both, and WinDVD should be renamed to FailBluray. They're so lazy with patches. PowerDVD gets patched at least once a month, but the team behind WinDVD is horrible. Like someone else said, it's slightly better for regular DVD playback. That's it.